This invention relates to a process of making a composite strip for producing contact members, for example, a micromotor brush, a contact member including one made by the process and a composite strip, for producing the contact member, including a strip when made by the process, and particularly, though not exclusively, to a contact member and its strip material capable of operation without producing sparks.
This invention also relates to a method of manufacturing the contact member and the contact member strip material.
Conventionally, when a brush or other contact member is operated, sparks are produced, thereby fusing its contact point. To solve this problem, a known contact point comprises carbon, and following two methods of manufacturing the contact member by using carbon have been proposed.
In a first proposed method, carbon powder, a mixture powder of silver and carbon, or a mixture powder of copper and carbon is processed using a press into pieces having a desired configuration, and the pieces are then sintered. These sintered metal pieces are installed, and caulked in position, into engaging bores formed in a nickel silver plate or other metal base plate, thereby manufacturing motor brushes.
In a second proposed method, a mixture of silver, palladium and carbon is press-molded into small chips and the chips are sintered. As shown in FIG. 4A, such chips P1 are aligned on a nickel silver coil P2. The nickel silver coil P2 is clad with the chips P1 through cold rolling, thereby forming a contact member strip material P3. Subsequently, as shown in FIG. 4B, the contact member strip material P3 is cut into contact members each having a desired width. Thus motor brushes P4 are manufactured.
The aforementioned first method requires a step for embedding each sintered piece into each engaging bore in the nickel silver plate and this makes it difficult to manufacture small contact members like micromotor brushes. Furthermore, each sintered piece needs to be thick enough to be caulked and properly secured in each engaging bore. Each resulting motor brush has a large and heavy structure which generates vibration and noise. This method is inappropriate for manufacturing brushes for a micromotor having allowable current of 100 mA or less. On the other hand, the allowable current of the micromotor is generally restricted to 100 mA or less by the difficulty of securing small sintered pieces in the engaging bores using caulk. In view of the problems, the control of sparks in micromotors using carbon cannot be expected. Even when large contact members are manufactured by this method, the manufacturing steps of embedding the sintered pieces into the engaging bores in the nickel silver plate and caulking the pieces in position involve intricate handling of components. As a result, the manufacturing of inexpensive products in large quantities cannot be attained by this method.
In the second proposed method, as shown in FIG. 4A, when the sintered chips P1 are arranged on the nickel silver coil P2 and are then rolled, discontinuities P5 are formed among the chips P1. Therefore, as shown in FIG. 4B, when the nickel silver coil P2 is processed with a press into the motor brushes P4, a contact point P6 has discontinuities P5, and provides unreliable contact. If the motor brushes P4 having large discontinuities P5 are eliminated from the manufactured motor brushes P4, a yield will decrease. Furthermore, the second method involves intricate steps of sintering the chips P1 beforehand, and arranging and cladding the chips P1 on desired positions of the nickel silver coil P2. Such steps cannot be easily conducted continuously.
It is also known to produce contact members from a strip material comprising a metal strip clad with another metal strip. When these contact members are manufactured, as shown in FIG. 9A, a surface metal strip P20 is first laid on a base metal strip P10. Subsequently, as shown in FIG. 9B, the base metal strip P10 with the surface metal strip P20 is cold-rolled or hot-rolled with rollers P30 to join the base metal strip P10 and the surface metal strip P20 to each other to form the strip material. Consequently, the configuration of the contact members resulting from the strip material is limited. The strip material is inappropriate for manufacturing quad flat packages provided with terminals on their peripheries. When a strip material clad with a surface metal layer having various configurations other than the strip one is formed, the surface metal strip P20 is cut beforehand into desired configurations, and is then secured onto desired positions on the base metal strip P10 by spot welding, prior to the step of rolling with the consequent additional steps of preparatory cutting and spot welding being required. Consequently, the contact members clad with the surface metal layers of the desired configurations cannot be easily manufactured continuously, precisely and in large quantities.